The present invention relates generally to combustors of aircraft gas turbine engines, and in particular to a cowl for an annular combustor which may be removed and replaced while components of the combustor remain assembled.
In a gas turbine engine, pressurized air is provided from a compressor to the combustor where it is mixed with fuel and burned. One type of combustor in widespread use is arranged in an annular configuration, where flame is contained in a hollow combustion chamber defined by co-annular inner and outer liners, with an annular dome plate interconnecting the liners at their upstream ends. The dome plate, referred to as a dome, contains a plurality of circumferentially spaced carbureting assemblies for mixing fuel and air and introducing the mixture into the chamber. Flow of pressurized air into the combustor is typically regulated by a fixed cowl which is mounted on the combustor in position upstream of the dome, where it defines an area across the entrance of the dome which is open to flow. The cowl divides air into a central stream which enters the carbureting assemblies and cooling streams which flow along the inner and outer liners to protect the combustor and turbine from heat damage. The cowl may include two separate annular rings, such as radially inner and outer cowls, or it may be formed in one piece.
The cowl, dome, inner liner, and outer liner are separate piece components which are assembled together with a set of circumferentially-spaced fasteners. The components are made separate to improve repairability and maintainability. Typically each fastener simultaneously connects three of the components, extending through commonly-aligned fastener holes in the cowl, dome, and one of the two liners.
Assembly of the combustor components is a detailed, time-consuming process because of the need for precision. Relative angles and spacing between the dome and the inner and outer liners are critical parameters that must be controlled to a close tolerance. Deviations from intended dimensions can produce variations in flame location and cooling stream effectiveness that decrease combustion performance and component durability. Accordingly, when the combustor is initially assembled, special tooling is required to establish precise dimensional control and proper relative positioning between the dome and liners. Such tooling is expensive and not widely available.
Unfortunately with current design approaches, when a cowl is removed for maintenance or replacement, its removal requires full disassembly of the combustor. The entire set of fasteners must be removed to separate the cowl from the remainder of the assembled combustor. Thus, when the fasteners are removed in order to replace a cowl, the dome and liners are freed from the assembly and their precise dimensional relations are lost. Reassembly requires that the parts be shipped to a facility having adequate special tooling. These steps are time-consuming and expensive.
A cowl according to the present invention directs flow of air entering a combustor of a gas turbine engine and is removable from the combustor without disassembling the combustor. The combustor has an annular, hollow chamber defined by an annular dome at an upstream end of the chamber, an inner liner extending downstream of the dome at a radially inner side of the chamber, an outer liner extending downstream of the dome at a radially outer side of the chamber, and a plurality of fasteners for attaching the dome, inner liner, and outer liner in an assembled condition. The dome has a plurality of circumferentially spaced first fastener holes, and the inner and outer liner each having a plurality of circumferentially spaced second fastener holes generally alignable with the first fastener holes forming pairs of first and second holes for receiving the fasteners. The cowl comprises an annular cowl body for guiding flow of air entering the combustor. A mounting rim on the cowl body attaches the cowl to the combustor in an operative position wherein the cowl body extends upstream of the dome. The mounting rim has a plurality of circumferentially spaced third fastener holes generally corresponding with the pairs of first and second holes. The third fastener holes are alignable with the corresponding pairs in the operative position to receive the fasteners commonly and simultaneously through first, second, and third fastener holes. At least one notch is in the mounting rim having an edge defining the notch and an open mouth. The notch is sized larger than a third fastener hole and configured such that when the cowl is in the operative position, the notch is aligned with a corresponding pair of first and second fastener holes. The edge of the notch is spaced outwardly from the holes such that one of the fasteners is receivable in the pair of first and second holes without engaging the mounting rim. The notch allows the cowl to be installed on or removed from the operative position while the dome, inner liner, and outer liner are held in the assembled condition.
In another aspect, a combustor assembly according to the present invention is for a gas turbine engine. The combustor comprises a hollow combustion chamber generally annular in shape and defined by a forward annular dome and a liner downstream of the dome. A plurality of fasteners extend through aligned holes in the dome and liner for connecting the dome and liner at circumferentially spaced locations. A cowl body having a generally uniform annular shape is mountable on the dome and liner at a mounted position. The cowl body has a plurality of circumferentially spaced fastener holes extending therethrough generally corresponding to the aligned holes in the dome and liner for receiving the fasteners to connect the cowl body to the dome and liner. At least one notch in the cowl body is sized sufficiently larger than a corresponding at least one fastener to permit the cowl body to be moved to or removed from the mounted position while the at least one corresponding fastener remains in position for connecting the dome and liner to one another.
In still a further aspect, a method according to the present invention removes a cowl from a combustor assembly of a gas turbine engine while the combustor remains assembled. The combustor has an annular, hollow chamber defined by a dome at an upstream end of the chamber, an inner liner extending downstream of the dome at a radially inner side of the chamber, and an outer liner extending downstream of the dome at a radially outer side of the chamber. The cowl is mountable on the combustor assembly in an operative position for regulating flow of air entering the chamber with a first set of fasteners commonly and simultaneously extending through aligned fastener holes in the cowl, dome, and one of the liners. The combustor assembly has a second set of fasteners extending through aligned fastener holes in the dome and one of the liners and free from engagement with the cowl. The second set of fasteners is generally aligned with notches formed in the cowl. The method comprising the steps of removing the first set of fasteners while leaving the second set of fasteners in place, and separating the cowl from the combustor assembly while the second set of fasteners holds the dome and liner connected to one another.
Other features of the present invention will be in part apparent and in part pointed out hereinafter.